1. Field
The present invention relates to the transmission and reception of broadcast databurst messages within a telecommunications system. More particularly, the present invention relates to a novel and improved method and apparatus for increasing the standby time of the receiver of broadcast databurst messages in a wireless telecommunications system.
2. Background
The cdma2000 cellular telephone standard proposal issued by the Telecommunications Industry Association (TIA), entitled “cdma2000 Series TIA/EIA/IS-2000,” published in August of 1999, hereinafter referred to as cdma2000, uses advanced signal processing techniques to provide efficient and high quality phone service, and is incorporated herein by reference. For example, a cdma2000 compliant cellular telephone system utilizes decoding, error detection, forward error correction (FER), interleaving and spread spectrum modulation in order to make more efficient use of the available radio frequency (RF) bandwidth, and to provide more robust connections. In general, the benefits provided by cdma2000 include longer talk time and fewer dropped calls when compared to other types of cellular telephone systems.
To conduct communications in an orderly manner, the cdma2000 standard provides a set of highly encoded channels over which data having different functions is transmitted. These highly encoded channels include one or more full paging channels, for carrying paging messages that notify cellular telephones or other types of wireless terminals, hereinafter referred to as remote stations, that an incoming request to communicate is pending. The full paging channel is further described below. Additionally, cdma2000 provides for a channel that is non-highly encoded, such as the quick paging channel further described below, to extend the standby time of remote stations. A new version of cdma2000, often referred to as cdma2000 Release A, is currently in ballot. The ballot version of cdma2000 Release A can be found in the December 1999 versions of following six TIA documents: PN-4693, PN-4694, PN-4695, PN-4696, PN-4797, and PN-4898. Each of these documents is incorporated herein by reference. This balloted version of cdma2000 Release A is hereinafter referred to as cdma2000A. cdma2000A introduces the Forward Common Control Channel (F-CCCH) and the Forward Broadcast Channel (F-BCCH). Whereas the full paging channel of cdma2000 uses a full paging channel to carry both general page messages (discussed below) and broadcast databurst messages, cdma2000A uses the F-CCCH to carry the general page messages, and uses the F-BCCH to carry broadcast databurst messages. The present invention is directed both at cdma2000 systems and at cdma2000A systems.
FIG. 1 is a block diagram of a simplified cellular telephone system that may be used to implement the present invention. Remote stations such as remote stations 10 (typically cellular telephones) are located around base stations 12. The remote stations 10a and 10b are in an active mode and are therefore interfacing with one or more base stations 12 using radio frequency (RF) signals modulated in accordance with the CDMA signal processing techniques of the cdma2000 standard. A system and method for modulating RF signals in accordance with CDMA modulation is described in U.S. Pat. No. 5,103,459 entitled “System and Method for Generating Signal Waveforms in a CDMA Cellular Telephone System” assigned to the assignee of the present invention and incorporated herein by reference. The other remote stations 10 are in standby mode and are therefore monitoring either a full paging channel for page messages indicating a request to communicate, or they are monitoring a quick paging channel for indicator bits indicating whether a message is expected on a full paging channel. An exemplary quick paging channel is given in U.S. Pat. No. 6,421,540, issued Jul. 16, 2002, entitled “A Method And Apparatus For Maximizing Standby Time Using A Quick Paging Channel,” which is a continuation-in-part of U.S. Pat. No. 6,393,295, filed Jul. 9, 1997 entitled “Dual Event Slotted Paging”, which is a continuation-in-part of U.S. Pat. No. 6,111,865, filed May 30, 1997 also of the same title, all of which are incorporated by reference herein.
In a preferred embodiment, each base station 12 generates forward link signals comprised of a set of forward link channels. The channels are established by a set of orthogonal Walsh codes. A Walsh code is used to modulate the data associated with a particular channel. The channels are categorized by function and include a pilot channel over which a phase offset pattern is repeatedly transmitted, a synch channel over which synchronization data is transmitted, including the absolute system time and the phase offset of the associated pilot channel, and traffic channels over which the data directed to the terminals 10 is transmitted. The traffic channels are normally assigned to transmit data to a particular remote station 10 for the duration of the interface with that particular base station. It should be understood that other types of codes and code lengths, along with other control channels, may be used in like systems.
Additionally, in accordance with one embodiment, one or more of the Walsh channels is designated as a quick paging channel, and one or more of the Walsh channels is designated as a full paging channel. The designation and operation of the full paging channel is preferably performed in accordance with the paging channel specified by the cdma2000 standard. Some methods and apparatus for performing paging substantially in accordance with the cdma2000 standard are described in U.S. Pat. No. 5,392,287 (the '287 patent) entitled “Apparatus And Method For Reducing Power Consumption In A Mobile Communications Receiver” and U.S. Pat. No. 5,509,015 (the '015 patent) entitled “Method And Apparatus For Scheduling Communications Between Transceivers” both assigned to the assignee of the present invention and incorporated herein by reference.
As described in the '287 and '015 patents, and as specified by the cdma2000 standard, the full paging channel is divided into time slots. The time slots are assigned to groups of remote stations 10. The assignment is performed based on the international mobile subscriber ID (IMSI) which is unique for each remote station 10, or other terminal identification information such as one or more mobile identification numbers (MIN). In alternative embodiments other identification information may also be used including the electronic serial number (ESN) of the remote station 10 or the temporary mobile subscriber ID (TMSI). The various types of identification information that may be used will be referred to hereinafter collectively as the mobile ID. The quick paging channels are also divided into time slots.
Characteristics of the full paging channel along with a detailed explanation of the quick paging channel are described in U.S. Pat. No. 6,421,540, issued Jul. 16, 2002, entitled “A Method And Apparatus For Maximizing Standby Time Using A Quick Paging Channel,” assigned to the assignee herein, and incorporated by reference herein. Paging schemes disclosed in U.S. Pat. No. 6,393,295, issued May 21, 2002, entitled “Dual Event Slotted Paging,” and in U.S. Pat. No. 6,111,865, issued Aug. 29, 2000, which are incorporated by reference herein, illustrate the basic implementation of a full paging channel in combination with a quick paging channel to provide terminal paging.
A full paging channel is a shared channel, meaning that the messages transmitted on this channel can be simultaneously decoded by many remote stations. The highly encoded full paging channel, which is divided into time slots of a predetermined duration called full paging slots, contain, amongst other messages, paging messages to indicate when there is an incoming call for a particular remote station. These paging messages can also be used to instruct a remote station to bring up a dedicated traffic channel to receive a databurst message that is directed to it. Databurst messages that are directed to an individual remote station are hereinafter referred to as a point-to-point databurst message, and are commonly called SMS (short message service) messages. “Joe, I got stuck in a meeting. I'll be home 30 minutes late for dinner,” is an example of the contents of the textual portion of a point-to-point databurst message.
In an alternate embodiment that follows the techniques of cdma2000A, the paging messages discussed above are transmitted on the F-CCCH in lieu of the full paging channel.
A quick paging channel is a shared channel that indicates to a remote station whether a page for that remote station is about to be transmitted on the paging channel. The quick paging channel is divided up into quick paging slots of a predetermined duration, which are preferably shorter than the duration of the full paging slots. In one exemplary embodiment each quick paging slot is 80 milliseconds (ms) in duration, while each full paging slot is 1.28 seconds. In the exemplary embodiment, a new full paging slot commences every 80 ms. Thus, in any 1.28 second period there are 16 full paging slots that partially overlap one another, and there are 16 quick paging slots that do not overlap each other. In the exemplary embodiment, quick paging slots are associated with full paging slots with the following one-to-one correspondence. Each quick paging slot that terminates is associated with the next full paging slot that commences after its termination.
To help clarify, please see FIG. 2. In FIG. 2, the top row is representative of the quick paging slots, each of an exemplary 80 ms duration, and wherein the next quick paging slot starts immediately after another finishes. The middle row, which can be referred to as the FPA slot cycle, is representative of a set of full paging slots that repeat on exemplary 1.28 second boundaries. The third row, which can be referred to as the FPB slot cycle, is representative of another set of full paging slots that repeat on exemplary 1.28 second boundaries. The timeline on the bottom shows that:                full paging slot FPA1 starts at 0.1 second (100 ms)        full paging slot FPB1 starts at 0.18 seconds (180 ms)        full paging slot FPA2 starts at 1.38 seconds (1380 ms)        full paging slot FPB2 starts at 1.46 seconds (1460 ms)        full paging slot FPA3 starts at 2.66 seconds (2660 ms)        full paging slot FPB3 starts at 2.74 seconds (2740 ms)        
FIG. 2 also shows the time slots for various quick paging. In FIG. 2,                at point 120, time 0, begins quick paging slot 1        at point 122, time 80 ms, quick paging slot 1 terminates        at point 124, time 160 ms, quick paging slot 2 terminates        at point 126, time 240 ms, quick paging slot 3 terminates        at point 130, time 1360 ms, quick paging slot 17 terminates        at point 132, time 1440 ms, quick paging slot 18 terminates        at point 140, time 2640 ms, quick paging slot 33 terminates        at point 142, time 2720 ms, quick paging slot 34 terminates        
Because quick paging slot 1 terminates at point 122 (time 80 ms), it is associated with FPA1, the next full paging slot to begin after time 80 ms. Likewise, because quick paging slot 2 terminates at point 124 (time 160 ms), it is associated with full paging slot FPB1, the next full paging slot to begin after time 160 ms. By the same reasoning, quick paging slot 17 is associated with full paging slot FPA2, and quick paging slot 18 is associated with full paging slot FPB2.
As can be seen in FIG. 2, there is a delta time between the termination of a quick paging slot and the commencement of the full paging slot with which it is associated. This delta time exists to allow the remote station time to switch from monitoring the uncoded quick paging channel to monitoring the highly encoded full paging channel. In cdma2000, and in the exemplary embodiment shown in FIG. 2, this delta is 20 ms. However, the delta can be a lower value (as low as a 0 ms delta) or a higher value in alternate embodiments.
Each quick paging slot contains indicator bits that are used to indicate to remote stations the remote stations for which a page will be transmitted. When an indicator bit is set for a particular remote station in a quick paging slot, a page message is subsequently transmitted during the full paging slot that is associated with that quick paging slot. For example, referring to FIG. 2, if indicator bits were set in quick paging slot 2 such that it indicated that a page would be sent to a particular remote station 10c (not shown), then a page would be transmitted to the IMSI of remote station 10c during full paging slot FPB1.
In an exemplary embodiment, there are 384 bits in each quick paging slot of 80 ms. Each quick paging slot is subdivided into a first 40-ms section and a second 40-ms section, each of 192 bits. For the purpose of redundancy, each bit transmitted as “on” in the first section has a corresponding bit transmitted as “on” in the second section. Likewise, each bit transmitted as “off” n the first section has a corresponding bit transmitted as “off” in the second section. The two corresponding bits are hereinafter referred to as bit-pairs. Each time a remote station is going to monitor a quick paging slot, the hash function of the remote station will take system time as one input and will yield a number representative of the incoming page bit indicator to monitor in the first 192 bits. The hashing function is also used to determine the other bit in the bit-pair that needs to be monitored in the second group of 192 bits. Put another way, a bit location X, in the first 192 bits, and a bit location Y, in the second 192 bits will be determined by each remote station for each quick paging slot that it monitors. The remote station can monitor bit X and bit Y on the quick paging slot to determine whether or not it should look for an incoming page on the full paging channel.
FIG. 3 is a representation of an exemplary quick paging channel slot of two sections. In the exemplary embodiment, each quick paging channel slot is 80 ms in duration and is comprised of 384 bits. In the exemplary embodiment, the quick paging channel slots are divided equally into two sections of 40 ms, each containing 192 bits. Although Quick Paging Slot (QPS) (see diagram) has a value of 384 in the exemplary embodiment, the value of QPS, as well as the duration of the quick paging slot, can take other values in alternate embodiments.
Point 210 is the location of the first bit in the first section of the quick paging slot. Point 214 is the location of the last bit in the first section of the quick paging slot. Point 212 is the location of a hashed bit location X, which is located somewhere in the first section of QPS/2 bits.
Point 220 is the location of the first bit in the second section of the quick paging slot. Point 224 is the location of the last bit in the second section of the quick paging slot. Point 222 is the location of a hashed bit location Y, which is located somewhere in the second section of QPS/2 bits. Both X and Y were determined using the same IMSI_S as an input, and therefor X and Y constitute a bit-pair of equivalent values. cdma2000 uses an instance of this embodiment, wherein an 80-ms slot contains 192 bit-pairs (QPS=384). Of the 192 bit-pairs, 2 bit-pairs, corresponding to the first two bits in each 40 ms section, are reserved for future use. The remaining 190 bit-pairs correspond to 190 unique hash values, and can be set to either on or off to indicate to remote stations whether or not to monitor a full paging channel slot associated with a quick paging channel slot. One skilled in the art would realize that other embodiments are available, such as embodiments that do not pair the bits for redundancy, and thus allow 384 bit locations to be uncorrelated with one another. Additionally, in alternate embodiments, more or fewer bits could be transmitted in quick paging slots of various durations.
In discussing quick paging slots and full paging slots, it should be noted that any given remote station is associated with exactly one cycle of full paging slots. A ‘cycle’ is a group of full paging slots that begin and end at substantially the same time. For instance, referring to FIG. 2, the second row (containing slots FPA1, FPA2, and FPA3) are one cycle of slots, while the third row (containing slots FPB1, FPB2, and FPB3) are another cycle of slots. These cycles are continuous.
Given that a remote station is only associated with one cycle of slots, it is efficient for a base station to only transmit indicator bits for a given remote station in the quick paging slots that terminate just prior to the transmission of the full paging slots with which a remote station is associated. It thus follows that any given remote station is associated only with the quick paging slots that terminate just prior to the commencement of each full paging slot in that remote station's slot cycle. For example, referring to FIG. 2, a remote station that is associated with the FPB slot cycle is associated with slots 2, 18, 34, and all other multiples of 2+16*K. Remote stations only need to monitor the quick paging slots with which they are associated.
As incorporated into the cdma2000 standard, the base station and the remote station use a hashing function to determine which indicator bits of the quick paging channel are to be associated with each individual remote station. Each remote station has a unique International Mobile Station Identifier (IMSI) assigned to it with which it registers to the base stations. The hashing function uses as one input IMSI_S (the short IMSI, which is the last 10 bits of the IMSI in cdma2000), and thus the hashing function has a unique input for each remote station. In cdma2000, the hashing function also uses system time as an input into the hash function. Thus, different indicator bits are set for a particular remote station depending on the time of transmission. The receiving remote station is able to use the same inputs to its hashing function such that it knows which indicator bits to examine in any particular quick paging slot.
By examining the indicator bits that the hash function yields, a remote station can tell by quickly looking at one or more indicator bits on the quick paging channel whether or not there will be a message directed to it in the next slot of the full paging channel. Because monitoring a small group of one or more indicator bits on a quick paging channel, which uses simple on-off keying (OOK), requires much less energy than monitoring a message of many bits on a highly encoded full paging channel, a remote station is able to conserve power when using a quick paging channel to monitor for pages. Thus remote stations are able to increase their standby time when using a quick paging channel to monitor for incoming pages.
Today, a large portion of databurst messages transmitted in commercial wireless telephone systems, are point-to-point databurst messages. As mentioned above, point-to-point databurst messages can be sent to remote stations by first transmitting an incoming page message in order to set up a transmission channel for the subsequent transmission of the databurst message. Thus, the use of the quick paging channel can increase standby time for remote stations configured to receive point-to-point databurst messages.
cdma2000 and its predecessors (the family of Telecommunication Industry Association (TIA) protocols known as IS-95, IS-95A, and IS-95B) also support broadcast databurst messages. Broadcast databurst messages, hereinafter referred to as broadcast messages, are databurst messages that are directed to a group of mobiles. An example of the contents of a broadcast databurst message, commonly called a broadcast SMS message by those skilled in the art, is a text message stating, “New call forwarding plans available; hit *611 to speak to a customer service representative for details.” Although some broadcast messages may be sent to all subscribers, there are also means to send broadcast messages to various groups of remote stations based upon the preferences that each individual subscriber has. cdma2000 currently has reserved support for 2 16 categories of broadcast messages, a small subset of which is currently defined. These broadcast categories are discussed in the document), entitled “Short Message Service for Spread Spectrum Systems ANSI/TIA/EIA/IS-637A,” published in September of 1999, incorporated herein by reference, wherein the broadcast categories are referred to as service categories.
Remote stations can be configured to receive only broadcast messages of the categories in which a particular subscriber is interested. For instance, if sports were a category, a given remote station would only receive broadcast messages of the sports category to which the remote station was subscribed. Likewise, if traffic was a category, a given remote station would only receive broadcast messages of the local traffic updates category to which the remote station was subscribed. “TRAFFIC REPORT: Highway 8 North backed up at Main Street due to accident. Expect a 40 minute delay,” is an example of the text of broadcast message that is only directed to remote stations that have been configured to receive a category of broadcast messages that contain traffic information.
Although the method of monitoring a quick paging channel in cdma2000 allows a remote station to conserve power when attempting to monitor for a point-to-point databurst message by using the quick paging channel to monitor for incoming pages directed at its IMSI, this method does not work for the reception of broadcast messages. The reason it does not work for broadcast messages is that a broadcast message is not directed at the remote station of one subscriber, as is a point-to-point message, but is rather directed to all remote stations configured to receive broadcast messages of a particular category. As there is no correlation between the IMSIs or remote stations and the categories of broadcast messages to which they are configured to receive, another method was developed to receive broadcast messages.
Presently, a method has been developed to monitor for broadcast messages. The method uses the general page message (GPM). Besides containing incoming page notifications for individual remote stations, a GPM can contain a listing of broadcast message categories to be transmitted, the channels on which they are to be transmitted, and the time slots during which each one will be transmitted. Each indication of when and on what channel a particular category of broadcast message will be transmitted is hereinafter referred to as a broadcast pointer. In relation to a particular remote station configured to receive a set of one or more categories of broadcast messages, a broadcast pointer of interest is a broadcast pointer that references a category in the aforementioned set of categories. A remote station that is configured to receive broadcast messages will periodically monitor the GPM messages transmitted at the beginning of its full paging slots. Although the GPM messages are not diagrammed in FIG. 2, in an exemplary embodiment, the GPM are at the beginning of the full paging slots. In cdma2000A, the GPM messages are monitored within the first 80 ms of each full paging slot on the F-CCCH. Because of the methodology that the base station uses to transmit GPMs, the remote station need only monitor GPM messages during the first 80 ms of the remote station's full paging cycle. A remote station may be configured to monitor the GPM messages toward the beginning of every full page slot in its slot cycle, or it may be configured to monitor the GPM messages at the beginning of one out of every N full page slots. The more infrequently it monitors for GPMs with broadcast information, the less power the remote station expends. The broadcast slot cycle index is a numerical value that corresponds to the frequency with which a remote station monitors for GPMs with broadcast information. The higher a remote station's broadcast slot cycle index, the less frequently a remote station monitors for GPMs with broadcast information.
In cdma2000, the GPM messages are transmitted on the full paging channel and reference broadcast messages at a subsequent time slot on the same full paging channel. In cdma2000A, the GPM messages are transmitted on a F-CCCH, and reference broadcast messages at a subsequent time slot on a F-BCCH.
As many users do not need to receive broadcast messages right away, remote stations are often configured with a large broadcast slot cycle index. In such cases, the remote station doesn't monitor for GPMs with broadcasts very often, and thus conserves much battery power. In fact, as of present, there may be many remote stations configured not to receive broadcast messages altogether. However, with the information explosion, it is thought that more users will begin to demand to receive broadcast messages of various categories with very little delay. In such a situation, wherein a user would likely demand a small broadcast slot cycle index, the power consumption inefficiencies of the above broadcast method scheme will become apparent. What is needed is a method and apparatus for maximizing standby time in remote stations configured to receive broadcast databurst messages.